It is well known to provide an apportioning device for fuel which is operated according to the amount of fresh air provided through the suction pipe of an internal combustion engine in connection with a measuring device for the amount of apportioned fuel. A throttle element in the supply line to the fuel supply mechanism is activated by an air volume meter, and by means of a differential pressure valve, the pressure differential on the cross-section released by the throttle element is maintained constant. The cross-section controlled by the throttle element in the fuel supply line is of slit-like shape so that the position of the throttle element is proportional to the flowing amount of fuel. The position of the throttle element is converted into a voltage corresponding to the flow by an inductance transducer. The fuel is advanced by the difference of pressure between the supply pressure and the pressure existing inside the suction pipe at the fuel outlet. This device can only be realized in connection with the corresponding apportioning device, and it is therefore applicable only in a limited manner to the measuring of fluids.